Piezoelectric pump

ABSTRACT

A pump body is provided including at least one inlet valve, at least one outlet valve, a substantially rigid top portion, a substantially rigid bottom portion, and collapsible side portions. The pump body also includes a base on or in the bottom portion and defining a rotational axis extending from the bottom portion. The pump body further includes a rotor shaft disposed along the rotational axis within the enclosure, a first end of the rotor shaft mechanically and rotatably coupled to the base, and a second end of the rotor shaft providing a cam surface for engaging the top portion and operable to cause motion of the top portion response to rotation of the rotor shaft. The pump body also includes at least one piezoelectric actuator engaging a surface of the rotor shaft, the piezoelectric actuator configured to cause the rotation of the rotor shaft.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. patent application Ser. No. 12/639,232, entitled “PIEZOELECTRIC MOTOR WITH HIGH TORQUE”, filed Dec. 16, 2009, and U.S. Provisional Application Ser. No. 61/149,941, entitled “PIEZOELECTRIC CORRUGATED-PISTON MICROPUMP”, filed Feb. 4, 2009, which are herein incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to pumping devices, and more specifically to piezoelectric pump devices for delivering fluids.

BACKGROUND

Conventional motorized piston-based micropumps for various types of fluids have been constructed using electromagnetic or pneumatic motors. More recently, interest has shifted toward micropumps that use piezoelectric actuators. Micropumps based on piezoelectric actuators have the potential of being less cumbersome, consuming less power, and being less noisy as compared to more conventional designs. Piezoelectric micropumps typically comprise a diaphragm that is driven by a piezoelectric element. The diaphragm is operatively associated with an air pump chamber which has communicating inlets and outlets in the pump housing or body. In such configurations, bending piezoelectric actuators are arranged against the diaphragm. Consequently, when the piezoelectric actuators are stimulated to have bending vibrations, the movement of the actuator results in movement of the diaphragm. This movement of the diaphragm leads to a cyclical change in the volume of the air pump chamber. One limitation of the arrangement described herein is that the bending actuators are generally not capable of providing a significant amount of linear displacement. As a result, the maximum flow and pressure these pumps can provide is typically limited.

SUMMARY

Embodiments of the present invention describe piezoelectric pumps. In a first embodiment of the invention, a pump body is provided including at least one inlet valve, at least one outlet valve, a substantially rigid top portion, a substantially rigid bottom portion, and collapsible side portions. The pump body also includes a base on or in the bottom portion and defining a rotational axis extending from the bottom portion. The pump body further includes a rotor shaft disposed along the rotational axis within the enclosure, a first end of the rotor shaft mechanically and rotatably coupled to the base, and a second end of the rotor shaft providing a cam surface for engaging the top portion and operable to cause motion of the top portion in response to rotation of the rotor shaft. The pump body also includes at least one piezoelectric actuator engaging a surface of the rotor shaft, the piezoelectric actuator configured to cause the rotation of the rotor shaft.

In a second embodiment of the invention, a pump is provided. The pump includes at least one inlet valve, at least one outlet valve, a substantially rigid top portion, a substantially rigid bottom portion, and collapsible side portions. The pump also includes a base on or in the bottom portion and defining a rotational axis extending from the bottom portion. The pump further includes a rotor shaft disposed along the rotational axis within the enclosure, a first end of the rotor shaft mechanically and rotatably coupled to the base, and a second end of the rotor shaft providing a cam surface for engaging the top portion and operable to cause motion of the top portion response to rotation of the rotor shaft. The pump also includes an annular piezoelement polarized along its thickness and having opposing upper and lower surfaces and inner and outer rim surfaces, the annular piezoelement retained on the base about the rotational axis. Additionally, the pump includes one or more flexible pushers, each of the flexible pushers having a first end mechanically coupled to the annular piezoelement and a second end extending radially to contact the rotor shaft. The pump further includes a power supply configured to excite a first-order radial vibration mode in the annular piezoelement. In the pump, the flexible pushers cause a rotation of the rotor shaft responsive to excitation of the first-order vibration mode in the annular piezoelement.

In a third embodiment of the invention, a reciprocating piezoelectric drive system is provided. The system includes a rotor shaft having an axis of rotation aligned with the shaft and a base configured for supporting the rotor shaft along the axis of rotation. The system also includes at least one piezoelectric actuator configured to apply a rotational force on the rotor shaft transverse to the axis of rotation when the piezoelectric actuator is electrically excited. The system further includes a cam surface defined on a portion of the rotor shaft and a cam follower which engages the cam surface and configured so that a rotation of the rotor shaft causes a reciprocating linear motion of the cam follower.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-section of an exemplary piezoelectric pump body in accordance with an embodiment of the invention in an expanded position.

FIG. 1B is a cross-section of the exemplary piezoelectric pump body of FIG. 1A in a compressed position.

FIG. 1C is a cross-section view of the exemplary piezoelectric pump body of FIG. 1A through cutline C-C.

FIG. 2A is a cross-section side view of an annular piezoelement for a pump body in accordance with an embodiment of the invention in an unexcited state.

FIG. 2B is a cross-section side view of the annular piezoelement in FIG. 2A in an excited state resulting in radial expansion.

FIG. 2C is a cross-section side view of the annular piezoelement in FIG. 2A in an excited state resulting in radial compression.

DETAILED DESCRIPTION

The present invention is described with reference to the attached figures, wherein like reference numerals are used throughout the figures to designate similar or equivalent elements. The figures are not drawn to scale and they are provided merely to illustrate the instant invention. Several aspects of the invention are described below with reference to example applications for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the invention. One having ordinary skill in the relevant art, however, will readily recognize that the invention can be practiced without one or more of the specific details or with other methods. In other instances, well-known structures or operations are not shown in detail to avoid obscuring the invention. The present invention is not limited by the illustrated ordering of acts or events, as some acts may occur in different orders and/or concurrently with other acts or events. Furthermore, not all illustrated acts or events are required to implement a methodology in accordance with the present invention.

As described above, existing piezoelectric pumps provide a relatively low fluid flow rate and small differential pressures. In these systems, even though the piezoelectric actuator is directly acting against the diaphragm, the working amplitude of the diaphragm is relatively low as compared to electromagnetic or pneumatic pumps. In general, this amplitude is several hundred microns for most conventional piezoelectric actuators. As a result, the limited amplitude limits the capacity of such systems to provide a high air flow.

In other to overcome the limitations of conventional piezoelectric pumps, a new piezoelectric pump is provided. In particular, a piezoelectric pump is provided in which the vibrations of one or more piezoelectric actuators are used to cause a rotation of a cam surface against a diaphragm. In the various embodiments of the invention, the cam surface is configured to provide a displacement that is substantially greater than the displacement provided by the piezoelectric actuator alone.

Those skilled in the art will appreciate that the piezoelectric pump described herein is operable for pumping various types of fluids. The term “fluid”, as used herein, refers to any substance that tends to continually deform or flow under an applied shear stress (i.e., substances that tend to take on the shape of a container they are disposed in). Examples of fluids include gases, liquids, plasmas, and other substances that provide little or no resistance to a deformation force.

The various embodiments of the invention provide piezoelectric pumps with functional capabilities that are improved by at least one order of magnitude, as compared to conventional piezoelectric pumps. Therefore, piezoelectric pumps in accordance with the various embodiments of the invention can operate at the same or better level of performance as conventional pumps based on electromagnetic motors. Further, piezoelectric pumps in accordance with the various embodiments of the invention preserve all the advantages of conventional piezoelectric pumps: small size, low noise, and low power consumption. An exemplary design for such a piezoelectric pump is shown in FIGS. 1A, 1B, and 1C.

FIG. 1A is a cross-section of an exemplary piezoelectric pump body 100 in accordance with an embodiment of the invention in an expanded position. FIG. 1B is a cross-section of the exemplary piezoelectric pump body 100 in FIG. 1A in a compressed position. FIG. 1C is a cross-section of the exemplary piezoelectric pump body 100 in FIG. 1A along cutline C-C. As shown in FIGS. 1A and 1B, the exemplary pump body 100 includes a substantially rigid bottom base portion 102 and a diaphragm portion 104 defining the enclosing portions of pump body 100. The diaphragm portion 104 can include a substantially rigid top portion 106 and collapsible side portions 108. The collapsible side portion can be formed of a pleated and/or flexible material so as to permit the pump body to define a working chamber that can expand and contract in volume. The diaphragm portion 104 can further include at least one inlet valve 110, at least one outlet valve 112. In some embodiments of the invention, valves 110 and 112 can be located on top portion 106, as shown in FIG. 1. However, the various embodiments of the invention are not limited in this regard and such valves can be located in other portions of pump body 100. Further, any types of valves can be used in the various embodiments of the invention. However, to simplify the design and operation of pump body, valves 110 and 112 can be check valves, non-return valves, or any other type of one-way valves that allow fluid to flow in only one direction and that operate automatically based on a pressure differential.

The exemplary pump body 100 shown in FIGS. 1A and 1B is configured as a substantially cylindrical pump body. However, the various embodiments of the invention are not limited in this regard and the pump body 100 can be configured to have other shapes, including shapes that are non-cylindrical and asymmetric. Further, the top portion 106 and bottom portion 102 are shown as being substantially parallel and aligned along a same axis 120. However, the various embodiments are not limited in this regard. Rather, the top portion 106 and bottom portion 102 can be substantially non-parallel and/or can be aligned along different axes. That is a direction of motion of top portion 106 need not be perpendicular to bottom portion 102.

Additionally, although pump body 100 is illustrated in FIGS. 1A and 1B as including collapsible side portions 108 with predefined folds to form pleated portions for guiding compression of the side portions 108, the various embodiments of the invention are not limited in this regard. In other embodiments of the invention, collapsible side portions 108 can exclude such folded or pleated portions or can include other types of structures within or external to collapsible side portions 108 for guiding compression of side portions 108.

In the various embodiments of the invention, the pump body 100 basically operates as a bellows. That is, a force is applied on top portion 106 to deform side portions 108 and therefore reduce an expanded length L₁ of the pump body to a compressed length L₂. As a result, the volume of pump body 100 is reduced by an amount proportional to the difference in lengths (ΔL=L₁-L₂), causing fluid within the pump body 100 to be expelled via outlet valve 112. Afterwards, when a force is applied on top portion 106 to increase a distance between the top portion 106 and bottom portion 102, side portions 108 are undeformed. As a result, the volume of pump body 100 increased, causing fluid to be drawn into the pump body 100 via inlet valve 110. In the various embodiments of the invention, the deforming and undeforming of diaphragm portion 104 is achieved via the operation of a piezoelectric actuated rotating cam mechanism 114 operating on top portion 106, as described below.

As shown in FIGS. 1A and 1B, the cam mechanism 114 includes a base 116 formed on or within the bottom portion 102. In the exemplary embodiment in FIGS. 1A and 1B, the base 116 has an inverted t-shape with the center portion including an axial guide portion 118 that defines a rotational axis 120. Mechanically and rotatably coupled to the axial guide portion 118 is a rotor shaft 122 extending along the rotational axis 120 within the pump body 100. A first end 122 a of the rotor shaft 122 is configured for engaging with the axial guide portion. A second end 122 b of the rotor shaft 122 is configured to provide a cam surface 122 c for engaging top portion 106 and in particular an actuating member 130 extending from top portion 106, as described below. In particular, cam surface 122 c is configured to have variation in elevation E_(CAM). As a result, as cam surface 122 c rotates against top portion 106, the varying elevation provided by cam surface 122 c causes a motion of top portion 106 in at least a direction substantially parallel to the rotational axis 120.

In the various embodiments of the invention, rotor shaft 122 and base 116 can be fabricated using various types of materials. For example, some materials include metals, metal alloys, ceramics, or glass materials. In the case of metals and metal alloys, these can include ferrous and non-ferrous materials. Further, these can also include magnetic or non-magnetic materials. Further rotor shaft 122 and guide portion 118 can also be configured to accommodate one or more bearings to facilitate rotation of rotor shaft 122 in guide portion 118.

Rotation of the rotor shaft 122 is achieved via the use of a radial piezoelectric actuator 124. Piezoelectric actuator 124 can include one or more a piezoelectric elements 126 and one or more flexible pushers 128 mechanically attached thereto. In the example shown in FIGS. 1A-1C, a single, annular piezoelectric element is provided. However, the various embodiments are not limited in this regard and multiple piezoelectric elements can be provided instead. For example, the annular piezoelement element 126 can be divided into segments, as shown by the dotted lines in FIG. 1C. The pushers 128 in piezoelectric actuator 124 are arranged to primarily extend in a generally radial direction toward rotational axis 120 and physically contact a portion of rotor shaft 122. Further, pushers 128 are also arranged to extend at least partially in a direction of rotation. For example, as shown in FIG. 1C, the pushers 128 comprise a cantilever-type spring extending in a radial direction toward rotational axis 120 and in a direction of rotation 140 about rotational axis 120.

In operation, when pushers 128 move radially towards rotor shaft 122, pushers deform and begin to apply a restorative force against rotor shaft 122 via a friction contact. Since a portion of the pushers 128 also extends along a direction of rotation, the restorative force of the pusher 128 is preferentially applied in the direction of rotation 140. Therefore, once a sufficient deformation of pushers 128 has occurred, the aggregate restorative force of the deformed pushers 128 becomes sufficiently large to overcome any frictional forces between rotor shaft 122 and guide portion 118, causing rotor shaft 122 to rotate about rotational axis 120 in a direction 140. When pushers 128 move radially away from rotor shaft 122, the pushers 128 undeform and stop applying a force against rotor shaft 122. This process can then be repeated to maintain rotation of rotor shaft 122.

In the embodiment shown in FIGS. 1A and 1B, the contacted portion of rotor shaft 122 is the second end 122 b. However, the various embodiments of the invention are not limited in this regard and the pushers 128 can be configured to contact other portions of rotor shaft 122. In operation, the piezoelectric element 126 is coupled via a plurality of electrodes (not shown) to an alternating voltage source (not shown) to induce vibrations in the piezoelectric element 126. These vibrations are transmitted to the pushers 128 and cause rotation of the rotor shaft 122 due to the frictional force between the pushers 128 and the rotor shaft 122.

In the various embodiments of the invention, the piezoelectric element(s) 126 can be fabricated from piezoceramics selected from the group of piezoelectric lead-zirconate-titanate-strontium ceramics (PZT) materials. However, the present invention is not limited to the use of PZT materials. In other embodiments of the present invention, other types of piezoelectric materials can be used. Furthermore, the piezoelements can be polarized.

In the various embodiments of the invention, the pushers 128 can be configured in a variety of ways. For example, pushers 128 can be constructed from a variety of materials, including beryllium, copper, or plastic, to name a few. However, the various embodiments of the invention are not limited in this regard and pushers 128 can be construct using any other types or combinations of materials suitable for providing a cantilever-type spring. Further, pushers 128 can be attached to piezoelectric element 126 using a cement or solder material. However, the various embodiments of the invention are not limited in this regard and other attachment methods can also be used. For example, fastener devices can be used to mechanically couple pushers 128 to piezoelectric element 126. In another embodiment, at least one of pushers 128 and piezoelectric element 126 can include one or more attachment features to provide mechanical coupling.

In FIGS. 1A and 1B, pushers 128 are shown to be attached to a top surface of a piezoelectric element 126 and towards an outer edge (with respect to rotational axis) of a piezoelectric element 126. However, the various embodiments of the invention are not limited in this regard. Rather, any other arrangement of pushers 128 on piezoelectric element 126 can be used, provided that such arrangement results in a vibration of pushers 128 in a direction substantially perpendicular to the rotation axis 120. For example, in some embodiments of the invention, the pushers 128 can be disposed on or towards an inner edge (with respect to rotational axis) of a piezoelectric element 126. In yet other embodiments of the invention, depending of the configuration of pump body 100, the pushers 128 can be disposed on a bottom surface of piezoelectric element 126.

In some embodiments of the invention, the top portion 106 can includes an actuating member portion 130, as described above, for engaging the cam surface 122 c of rotor shaft 122. The actuating member portion 130 can include an extending portion 132 projecting from top portion 106 towards the cam surface 122 c of rotor shaft 122. The actuating member portion 130 also includes a cam-follower portion 134 for physically contacting the cam surface 122 c of rotor shaft 122. In the various embodiments of the invention, the components of actuating member portion 130 are fixed in position relative to the rotating cam surface 122 c.

In the various embodiments of the invention, actuating member portion 130 can be fabricated using various types of materials. For example, some materials include metals, metal alloys, ceramics, or glass materials. In the case of metals and metal alloys, these can include ferrous and non-ferrous materials. Further, these can also include magnetic or non-magnetic materials. In some embodiments of the invention, the cam-follower portion 134 can include one or more bearings for engaging the cam surface 122 c.

The pump body 100 operates as follows. First, mechanical vibrations are excited in each piezoelectric element 126 when the electrical power is applied to the piezoelement. These vibrations are transmitted to the pushers 128 and cause rotation of the rotor shaft 122 due to the frictional force between the pushers and the rotor, as described above with respect to FIG. 1C. As the rotor shaft rotates, the cam surface 122 c also rotates, causing the elevation of the portion of the cam surface 122 c in contact with cam-follower portion 134 to vary up to an amount equal to E_(CAM). As a result, the cam-follower portion 134 causes the top portion 106 to move.

Therefore, as the actuating member 130 moves upward, as shown in FIG. 1A, the top portion 106 also moves upward, causing side portions 108 to move toward an extended state. As a result, as volume of pump body 100 expands, the outlet valve 112 closes, and inlet valve 110 opens to draw fluid in. When the actuating member 130 moves downward, as shown in FIG. 1B, the top portion 106 also moves downward, causing side portions 108 to deform. In some embodiments of the invention, the downward motion of the top portion 106 can be achieved by inclusion of spring or other restorative element (not shown) for applying a force to deform side portions 108 and drawing top portion 106 downward as the elevation of the contacted portion of cam surface 122 c changes. In other embodiments of the invention, top portion 106 can be weighted such that the weight of top portion 106 causes the deformation of side portions 108 and motion of top portion 106. In yet other embodiments, cam surface 122 c can include a track or other guide and cam follower portion 134 can be configured to engage and follow the track as cam surface 122 c rotates. As a result of such processes, the volume of pump body 100 is decreased, inlet valve 110 closes, and outlet valve 112 opens to expel fluids from pump body 110. As the cam surface 122 c continues to rotate, top portion 106 oscillates between the expanded and compressed positions, resulting in pump body 100 continuously oscillating in volume and causing pumping of fluids.

In the exemplary embodiment shown in FIGS. 1A and 1B, actuating member portion 130 is shown as extending from a contact point 136 at a center of top portion 106 and being L-shaped to contact a portion of cam surface 122 c away from rotational axis 120 as rotor shaft 122 rotates. Such a configuration is provided for several reasons. First, if top portion 106 is substantially symmetrical about rotational axis 120, such a configuration allows cam surface 122 a to apply a displacement force via actuating member portion 130 to a center of mass of top portion 106. Further, such a configuration allows contact point 136 and rotor shaft 122 to be disposed along a same axis, allowing a more compact design of pump body 100. However, the various embodiments of the invention are not limited in this regard. In other embodiments of the invention, contact point 136 need not be L-shaped and can therefore be at a position that is not at the center of top portion 106. Further, in other embodiments of the invention, rotational axis 120 can be offset from a center of top portion 106. Therefore, contact point 136 need not be L-shaped to contact a portion of cam surface 122 c away from rotational axis 120.

As described above, motion of the rotor shaft in FIGS. 1A and 1B is achieved via piezoactuators comprising one or more piezoelements, each having one or more pushers extending therefrom and contacting the rotor shaft. In the various embodiments of the invention, the piezoactuators can be configured in a variety of ways. For example, in some embodiments, the piezoactuators 124 in FIGS. 1A and 1B can include one or more segments of piezoelectric material positioned about rotational axis on base 116. Therefore, a longitudinal wave perpendicular to the rotational axis and oriented along the radius can be excited in such segments, causing longitudinal vibrations that can be transferred to the pushers 128. The pushers 128 then oscillate against rotor shaft 122 and cause rotor shaft 122 to rotate, similar to the method described above with respect to FIG. 1C.

In another example, as shown in FIG. 1C, an annular or ring-shaped resonator operating in a radial vibration mode can be used for piezoelectric element 126. In general, the frequency of the radial mode of a ring-shaped resonator F_(r) ^(R) is described by the equation:

$\begin{matrix} {F_{r}^{R} = {\frac{1}{{ad}\; \pi}\sqrt{\frac{n^{2} + 1}{\rho \star s_{jk}}}}} & (1) \end{matrix}$

where d is an average diameter of the ring (in particular the diameter of the piezoelectric ring), s_(jk) is the coefficient of elasticity of the material (in particular the material of the piezoelectric ring), a is the form factor of the ring (in particular the form factor of the piezoelectric ring) which is determined experimentally, ρ is density of the material (in particular, density of the piezoelectric ring), and n is an integer≧0 and specifying the order of the vibrational mode. In the case of zero order radial vibrational mode (1) can be transformed into the equation:

F _(r) ^(R) =c _(p)/2×π[(R _(p) +r _(p))/2],  (2)

where c_(p) is the speed of propagation of sound waves in the material, R_(p) is the outside radius of the annular piezoelement, and r_(p) is the inner radius of the annular piezoelement.

In order to increase the maximum flow for the pump in FIGS. 1A and 1B the rotation speed of the motor needs to be increased. In general, an increase in the rotational speed is usually achieved via an increase in the diameter of the piezoresonator annular ring while the diameter of the rotor is kept constant. However, a significant disadvantage with this approach is that as the diameter of the annular piezoelement is increased, the frequency of the zero-order vibrational mode begins to approach frequencies that are audible by the human ear.

In such annular piezoelement, the decrease in frequency is typically compensated for by reducing the internal radius of the annular piezoelement, thus increasing the annular width of the annular piezoelement. The term “annular width” as used herein, refers to the difference between the inner and outer diameters of an annular piezoelement. This will lead to an increase in the excitation frequency according to equation (2), but in this case the system operates as a thick ring resonator (a thick ring here is defined by the annular width of the annular piezoelement) and the quality (Q) factor decreases rapidly. As used herein, the “Q factor” is a measure of the relationship between stored energy and rate of energy dissipation in resonator. Thus a high Q factor indicates a high efficiency resonator and a low Q factor indicates a low efficiency resonator. A similar situation arises when higher order radial excitation modes are used. In such instances, the Q factor of the annular piezoelement also decreases rapidly and the motor becomes less efficient.

Therefore, in some embodiments of the present invention, the maximum pump flow rates can be achieved by providing an annular piezoelement and selecting an operating frequency for the applied voltage so as to excite the first-order longitudinal mode of vibration radially along the annular width of the annular piezoelement. In particular, an operating frequency F_(r) ^(p)) for the excitation voltage can be provided that is described by the equation:

F _(r) ^(p) =c _(p)/2h,  (3)

where c_(p) is the speed of propagation of the sound waves in the annular piezoelement material and h is the annular width of the annular piezoelement (h=R_(p)−r_(p)).

Accordingly, excitation of the first order vibrational longitudinal mode can be achieved by configuring the annular piezoelement to have an outer radius (R_(p)) that is at least twice the inner radius (r_(p)) (i.e., R_(p)>2r_(p)) and an annular width (h) that is at least twice a thickness of said piezoelectric element (i.e. h>2H). Therefore, when excited using an alternating voltage having a frequency (F_(r) ^(p)) equal to c_(p)/2(R_(p)−r_(p)), the portions of the annular piezoelement at or near the inner rim and the outer rim surfaces of the annular piezoelement are operable to efficiently transfer oscillations of the annular piezoelement in the radial direction to the pushers to effect rotary movement of a rotor about the rotational axis with a significantly higher amount of torque than observed in conventional piezoelectric motors, including annular piezoelements. Accordingly, based on the relationships R_(p)>2r_(p) and h>2H for the piezoelement and the piezoelectric material (which specifies c_(p)), dimensions for the annular piezoelement for a particular excitation voltage frequency can be selected.

The resulting excitation of such an annular piezoelement is described in FIGS. 2A-2C. FIG. 2A is a cross-section side view of an annular piezoelement in an unexcited state. FIG. 2B is a cross-section side view of the annular piezoelement in FIG. 2A in an excited state resulting in radial expansion. FIG. 2C is a cross-section side view of the annular piezoelement in FIG. 2A in an excited state resulting in radial compression.

As shown in FIGS. 2A-2C, the annular piezoelement has dimensions R_(p) and r_(p) so that an excitation voltage with frequency F_(r) ^(p) corresponds to the frequency of the first longitudinal mode across the annular width (h) of the annular piezoelement. Prior to applying the excitation voltage, the annular width h of the piezoelement is unchanged, as shown in FIG. 2A. Once the excitation voltage is applied, deformation begins. As shown in FIG. 2B, a lateral deformation (−ΔH) can occur along the thickness (H) of the annular piezoelement. As a result of this initial lateral deformation and due to the elastic forces, at least some secondary deformation along the width of the annular piezoelement is formed. This is transformed into a longitudinal standing wave radial deformation with maximum amplitude of the vibrations at the positions of the outer rim A and inner rim B of the annular piezoelement, and minimum amplitude of the vibrations at the midpoint between A and B, such as point C. (Point C defines the median diameter of the ring, and determines the attachment points of the annular piezoelement to a stator.) The radial expansion of the annular piezoelement causes an increase in the annular width h, and this results in rims A and B moving in radially opposite directions by amounts Δh₁ and Δh₂, respectively, as shown in FIG. 2B As a result, the pushers located at or near A or B are radially displaced.

As the alternating excitation voltage is further applied to the annular piezoelement, compression of the width of the annular piezoelement can subsequently occur, as shown in FIG. 2C. In contrast to FIG. 2B, the radial compression, which is symmetrical in respect to the medium radius point C, decreases the annular width h. The radial compression of the annular piezoelement causes a decrease in the annular width h. This results in rims A and B moving in radially opposite directions by amounts −Δh₃ and −Δh₄, respectively, as shown in FIG. 2C. As a result, the pushers are displaced in an opposite radial direction.

An exemplary configuration for a pump in accordance with an embodiment of the invention will be described below. Although the calculations below are show for pumping gases, one of ordinary skill in the art will recognize that a similar set of calculations can be provided for configuring a pump in accordance with an embodiment of the invention to pump other types of fluids, such as liquids.

In the case of a gas, the value of E_(CAM) for the exemplary piezoelectric pump in FIGS. 1A-1C can be selected based on Boyle's law, which describes that the relationship between the pressure and the volume of gas in the pump body at the two positions shown in FIGS. 1A and 1B is given by:

P₁V₁=P₂V₂,  (4)

where P₁ and V₁ are the gas pressure and volume, respectively, for the configuration shown in FIGS. 1A and P₂ and V₂ are the gas pressure and volume, respectively, for the configuration shown in FIG. 1B. Therefore, assuming that pump body 100 is substantially cylindrical, D is the diameter of the cylinder and ΔL (i.e., the amount of linear movement during compression), the expanded volume V₁ may be written as:

V ₁ =V ₂ +S×ΔL,  (5)

where S is given by π(D/2)². Equation (4) can then be written as:

P ₁(V ₂ +S×ΔL)=P ₂ V ₂.  (6)

Therefore, if the increase in pressure after compression is ΔP, then P₂ can be expressed as:

P ₂ =P ₁ +ΔP,  (7)

and equation (6) can be rewritten as:

ΔP/P ₁=(S×ΔL)/V ₂  (8)

However, when pump body is extended:

V ₂ =S×L ₁.  (9)

Therefore, Equation (8) can then be reduced to:

ΔP/P ₁ =ΔL/L ₁  (10)

Accordingly, based on Equation (10), the elevation variation for the cam surface 122 c can be determined since E_(CAM)=ΔL. For example, if P1=15 PSI, ΔP=2 PSI, and L₁=15 mm, then ΔL=E_(CAM)=2 mm.

In addition to selecting E_(CAM), the maximum gas flow rate, Q, can be selected as well in the various embodiments of the invention. First, the volume of gas expelled during one cycle of movement is S×ΔL, as shown above in Equation (5). Therefore the full gas flow Q is given by the formula:

Q=(S×ΔL)×F  (11)

where F is the angular speed of rotation of the motor. Therefore, F can be expressed as:

F=Q/(S×ΔL).  (12)

Accordingly Equation (12) can be used to select an angular speed for the pump body to provide a desired flow rate. For example, if Q=240 cm³ per minute=4 cm³/s, the diameter of the pump is D=2.6 cm, so that S=π(D/2)²=5.3 cm², and ΔL=2 mm=0.2 cm, Equation (9) yields the estimate of the required angular speed as 3.8 rev/sec or 228 RPM.

Therefore, if the pump body 100 shown in FIGS. 1A and 1B is selected to have dimensions of D=26 mm and L=15 mm and ΔL is selected to be 2 mm (about 8 cm³ of volume displacement), a maximum pressure of 2 PSI and a maximum flow rate of 240 cm³ are achievable. Further, since only an angular speed of 228 RPM is needed to achieve this value of Q, any noise associated with the resulting frequencies are outside of the range of normal human hearing.

E_(CAM) and F can also be selected for other fluids, such as liquids. In the case of liquids, a needed head and discharge rate at an access point can be obtained. Such calculations are well-known to those of ordinary skill in the art and will not be described herein.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the spirit or scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above described embodiments. Rather, the scope of the invention should be defined in accordance with the following claims and their equivalents.

Although the invention has been illustrated and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and/or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.”

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 

1. A pump body comprising at least one inlet valve, at least one outlet valve, a substantially rigid top portion, a substantially rigid bottom portion, and collapsible side portions, said pump body further comprising: a base on or in said bottom portion and defining a rotational axis extending from said bottom portion; a rotor shaft disposed along said rotational axis within said enclosure, a first end of said rotor shaft mechanically and rotatably coupled to said base, and a second end of said rotor shaft providing a cam surface for engaging said top portion and operable to cause motion of said top portion response to rotation of said rotor shaft; and at least one piezoelectric actuator engaging a surface of said rotor shaft, said piezoelectric actuator configured to cause said rotation of said rotor shaft.
 2. The pump body of claim 1, wherein said top portion further comprises an actuating member extending from a contact point on said top surface and physically contacting said cam surface.
 3. The pump body of claim 2, wherein said actuating member is L-shaped.
 4. The pump body of claim 2, wherein at least one portion of said actuating members extends transverse to said motion axis.
 5. The pump body of claim 2, wherein said contact point comprises a center of said top portion.
 6. The pump body of claim 2, wherein said actuating member comprises at least one bearing for said contacting of said cam surface.
 7. The pump body of claim 2, wherein said rotational axis extends through said contact point.
 8. The pump body of claim 1, wherein said piezoelectric actuator comprises: a piezoelement configured for generating a longitudinal vibration in a radial direction towards said rotational axis; one or more flexible pushers, each of said flexible pushers having a first end mechanically coupled to said piezoelement and a second end extending in said radial direction and contacting said surface of said rotor shaft.
 9. The pump body of claim 8, wherein said piezoelement further comprises an annular piezoelement polarized along its thickness and retained on said base about said rotational axis.
 10. The pump body of claim 9, further comprising: a plurality of electrodes electrically coupled to upper and lower surfaces of annular piezoelement; and a power supply configured to excite a first-order radial vibration mode in said annular piezoelement.
 11. The pump body of claim 8, wherein said flexible pushers are mechanically coupled to said upper surface of said annular piezoelement.
 12. The pump body of claim 8, wherein a pusher material for the pushers is selected from the group consisting of beryllium, copper, and plastic.
 13. The pump body of claim 1, wherein said inlet and outlet valves are located on the top portion of said enclosure.
 14. The pump body of claim 1, wherein at least the rotor, and the actuating member comprise non-magnetic materials.
 15. The pump body of claim 14, wherein said rotor comprises ceramic or glass.
 16. The pump body of claim 14, wherein the actuating member comprises non-ferrous metals.
 17. The pump body of claim 1, wherein said collapsible side portions comprise one or more elbows.
 18. The pump body of claim 1, wherein said base comprises an axial guide portion extending from said base for said coupling of said rotor shaft.
 19. A pump comprising at least one inlet valve, at least one outlet valve, a substantially rigid top portion, a substantially rigid bottom portion, and collapsible side portions, said pump further comprising: a base on or in said bottom portion and defining a rotational axis extending from said bottom portion; a rotor shaft disposed along said rotational axis within said enclosure, a first end of said rotor shaft mechanically and rotatably coupled to said base, and a second end of said rotor shaft providing a cam surface for engaging said top portion and operable to cause motion of said top portion response to rotation of said rotor shaft; an annular piezoelement polarized along its thickness and having opposing upper and lower surfaces and inner and outer rim surfaces, said annular piezoelement retained on said base about said rotational axis; one or more flexible pushers, each of said flexible pushers having a first end mechanically coupled to said annular piezoelement and a second end extending radially to contact said rotor shaft; and a power supply configured to excite a first-order radial vibration mode in said annular piezoelement, wherein responsive to said exciting of said first-order vibration mode in said annular piezoelement, said flexible pushers cause a rotation of said rotor shaft.
 20. The pump of claim 19, wherein said flexible pushers are mechanically coupled to a portion of said annular piezoelement on or near one of said inner and outer rim surfaces.
 21. A reciprocating piezoelectric drive system comprising: a rotor shaft having an axis of rotation aligned with said shaft; a base configured for supporting said rotor shaft along said axis of rotation; at least one piezoelectric actuator configured to apply a rotational force on said rotor shaft transverse to said axis of rotation when said piezoelectric actuator is electrically excited; a cam surface defined on a portion of said rotor shaft; and a cam follower which engages said cam surface and configured so that a rotation of said rotor shaft causes a reciprocating linear motion of said cam follower.
 22. The reciprocating piezoelectric drive system according to claim 21, wherein said cam surface is aligned transverse to said axis of rotation.
 23. The reciprocating piezoelectric drive system according to claim 22, wherein said cam surface is an end face of said rotor shaft transverse to said axis of rotation.
 24. The reciprocating piezoelectric drive system according to claim 21, further comprising a bellows, said cam follower mechanically coupled to a first rigid portion of said bellows such that said reciprocating motion causes an internal chamber of said bellows to increase and decrease in volume.
 25. The reciprocating piezoelectric drive system according to claim 24, further comprising an inlet valve and an outlet valve in fluid communication with said internal chamber of said bellows.
 26. The reciprocating piezoelectric drive system according to claim 25, wherein said rotor shaft and cam follower are disposed within said internal chamber of said bellows.
 27. The reciprocating piezoelectric drive system according to claim 25, at least one piezoelectric actuator configured to apply a rotational force on said rotor shaft transverse to said axis of rotation when said piezoelectric actuator is electrically excited.
 28. The reciprocating piezoelectric drive system according to claim 21, wherein said piezoelectric actuator comprises: a piezoelement configured for generating a longitudinal vibration in a radial direction towards said rotational axis; one or more flexible pushers, each of said flexible pushers having a first end mechanically coupled to said piezoelement and a second end extending in said radial direction and contacting said surface of said rotor shaft.
 29. The reciprocating piezoelectric drive system according to claim 28, wherein said piezoelement further comprises an annular piezoelement polarized along its thickness and retained on said base about said rotational axis.
 30. The reciprocating piezoelectric drive system according to claim 29, further comprising: a plurality of electrodes electrically coupled to upper and lower surfaces of annular piezoelement; and a power supply configured to excite a first-order radial vibration mode in said annular piezoelement.
 31. The reciprocating piezoelectric drive system according to claim 8, wherein said flexible pushers are mechanically coupled to said upper surface of said annular piezoelement. 